A known antenna of the multiple focussed beams type with failure correction means is known. The front end of this antenna comprises a beam forming network (subsequently called a BFN) supplying input signals to a set of multiport amplifiers (subsequently called MPA). There are as many MPA as the maximum number of radiating feed used by any beam. Every beam uses one radiating feed belonging to each of the MPAs. The MPA has an input matrix separating signals corresponding to each input port, through an input matrix such that all beam signals are amplified by a set of high power amplifiers (subsequently called HPA) connected on the output side. Thus, independently of the beam power distribution between different input ports, an equal load is obtained for all HPAs that belong to the same MPA. Depending on the input port considered, the input matrix generates different relative phases at HPA inputs. An output matrix is connected to the output of HPAs and once again separates signal belonging to each input port, and applies them to the corresponding output port. This antenna transmit front end architecture is called multimatrix in the literature.
This antenna has HPA failure correction means. Thus, the antenna has redundant HPAs and redundancy circuits that will make the necessary switchings to replace a failed HPA in service by a redundant HPA. Thus, the total radio frequency power can be maintained.
There are several problems with this antenna. Redundancy circuits require a significant number of RF switches and redundant HPAs. Consequently, electrical losses, the mass, size, complexity, probability of failure and cost of the antenna are high. These disadvantages are more serious because the antenna is a mass that can be installed on a satellite and put into orbit.
Furthermore, high losses are caused by the accumulation of losses in the matrices, in the redundancy circuits, in wave guides, in insulators and in radiation filters, particularly in the Ku and Ka bands.
Due to the large size of the antenna, a wave guide or long coaxial cables are used to connect the antenna radiating feeds, leading to additional losses.
Furthermore, the antenna requires good phase and amplitude tracking between the different HPAs, so as to guarantee good isolation of RF beams. This problem increases with the operating frequency and is very acute in the Ka band. Consequently, phase and amplitude control tracking elements are required to correct phase and amplitude tracking errors due to temperature and aging. Furthermore, after each modification to the configuration of the redundancy circuit, phase and amplitude tracking of the MPA structure must be readjusted so as to guarantee good isolation of the RF beam.
Operation of HPAs in multi-carrier mode requires a reduction of the output back-off (OBO) power equal to more than 4 dB to obtain acceptable linearity performances. This problem is worsened by the fact that assignment of different powers to the different beams and due to the excitation dynamics of multiple radiating feeds contributing to forming each beam.
MPAs have been successfully used in the L and S bands in different missions. However, it is difficult to use the MPA concept at higher frequencies (Ku and Ka bands) because the problems mentioned above are further amplified. It is well known that phase and amplitude tracking errors are limited by the use of large MPAs (for example 16×16). However, redundant HPA amplifiers and the associated switching matrices are still necessary to maintain power and beam isolation within acceptable limits.